Chemoautotrophy drives plankton activity under the Ross Ice Shelf

In Antarctica, ice shelves fringe 75% of the coastline and cover >1.5 million km², creating distinct and largely unexplored marine environments. To uncover the biogeochemical role of under-ice shelf ecosystems and to predict how they might respond to future ice-shelf collapse, it is fundamental to identify and characterize those communities and their functioning. The Ross Ice Shelf (RIS), the largest ice shelf in the world, floats atop an 54,000 km³ocean cavity. The only previous study in which the seawater under the RIS was biogeochemically studied (J9 borehole) preceded the emergence of modern, molecular research approaches. Thus, the phylogenetic and functional diversity of microorganisms under RIS remains unknown. Four decades later, we used hot water to drill through ca. 400 m of ice shelf in order to examine the structure and function of this globally important environment. We combined rate measurements and rRNA amplicon sequencing with multi-omics (i.e., single cell genomics, meta-genomic, -transcriptomics and -proteomics). This revealed an active and diverse microbial ecosystem dominated by chemolithoautotrophy, where energy is obtained from a wide range of inorganic sources. Chemolithoautotrophy supported the heterotrophic community and food webs under the RIS, hence representing a system driven by dark carbon dioxide fixation, making the RIS presumably the largest chemolithotrophic system in the global ocean.